There has been used an organic EL device that for example includes, above a glass substrate, a display unit having an organic EL layer between an anode and a cathode.
In recent years, there has been a demand for organic EL display devices having excellent design and mobility. An organic EL display device having excellent design for example is that with a curved display unit. An organic EL display device having excellent mobility for example is that with reduced weight.
In response to the above demand, a technology has been proposed that uses, for an organic EL display device, a resin substrate (a resin film) that has flexibility and thus is bendable, instead of a glass substrate (for example, Patent Literature 1). However, a resin substrate typically does not function much as a barrier against moisture. For this reason, using a resin substrate leads to moisture intrusion into an organic EL layer through the resin substrate. This may result in a change in light-emission color, or even worse, in light emission incapability.
In view of this, a technology has been proposed that prevents moisture intrusion into the display unit (organic EL layer) by providing a hygroscopic layer between the resin substrate and the display unit to absorb/adsorb any moisture that may otherwise intrude into the display unit (for example, Patent Literatures 2 and 3).
The hygroscopic layer described in Patent Literature 2 has a configuration in which a hygroscopic film is sandwiched by a pair of inorganic films. The inorganic films are made of a material having a low moisture vapor transmission rate (indicates a degree of moisture transmission), whereby penetration of moisture into the hygroscopic layer is suppressed. Further, any moisture penetrating through the inorganic films is absorbed/adsorbed by the hygroscopic film.
The hygroscopic layer described in Patent Literature 3 has a configuration where a hygroscopic agent is mixed in an organic material, and an organic EL layer-side region of the hygroscopic layer contains the hygroscopic agent at a large amount.